Electric rectifiers employing semi-conductors



30, 1958 A. J. BLUNDELL 2,866,928

ELECTRIC RECTIFIEIRS EMPLOYING SEMI-CONDUCTORS Filed May 21, 1956INVE/VT'OR flLAN fouu BLU ELL y United States Patent ELECTRIC RECTIFIERSEMPLOYING SEMI-CONDUCTORS Alan John Blundell, Willoughby, near Rugby,England, assignor to The British Thomson-Houston Company Limited,London, England, a British company Application May 21, 1956, Serial No.586,243 Claims priority, application Great Britain May 23, 1955 4Claims. (Cl. 317-234) This invention relates to electric rectifiersemploying semi-conductors as the rectifying element, the contact withthe rectifying element being of the broad area P-N junction type.

In constructing electric rectifiers of the above type, it is essential,inter alia, to provide the rectifying element with an hermeticallysealed casing to obviate the deleterious effects of atmosphericconditions on the rectifying element, and to ensure that an undue risein temperature of the rectifying element does not occur either duringmanufacture or operation, and to reduce to a minimum the number ofsealing points required in constructing the enclosing envelope for theelement.

It is the object of the invention to provide a construction of electricrectifier which will satisfy these desiderata.

A P-N junction rectifier of the kind set forth, according to theinvention, comprises a base of a metal of good thermal conductivity, towhich the rectifying element is intimately secured at one face, aco-operating electrode extending from the other face of the element andterminating in a metal rod, a flanged metal annulus hermetically securedat its flange to the base, so as to encircle the element, an annularinsulating member which forms on the one hand, an hermetic joint to themetal annulus and, on the other hand, an hermetic joint to the rim of ablind metal sleeve provided with a central recess into i which extendsthe metal rod terminating the co-operating electrode, the rod being heldWithin the recess in, and electrical contact made to, the metal sleeveby pressing the wall of the recess on to the rod.

The enclosure for the rectifying element is thus constituted by theinner faces, or walls, of the base, the flanged metal annulus, theannular insulating member and the metal sleeve, all of which areintimately secured to adjacent members to form an hermetically sealedcasmg.

The invention will be better understood from a consideration of thefollowing description of the accompanying drawings, in which- Fig. 1 isa plan view of a rectifier constructed in accordance with the invention;

Fig. 2 is an elevation partly in section, to show the internalconstruction of the rectifier;

Fig. 3 is a view similar to Fig. 2 of a modified construction; and

Figs. 4 to 6 show three ways of mounting the rectifier in aheat-radiating fin.

Referring to Figs. 1 and 2, there is shown the rectifier as consistingof a base plate or member 1 of metal of high thermal and electricalconductivity, e. g. copper, to which the rectifying element 2 isattached. The base member 1 has secured to it a flanged metal annulus 3,to the upper rim of which is hermetically secured an in sulating member4. The member 4 is shown as formed with an internal shoulder into whichseats the flanged portions of a metal sleeve provided with a blind holeor recess 6. The base member 1, metal annulus 2, insulating member 3 andmetal sleeve 5, together form 2,866,928 Patented Dec. 30, 1958 anhermetic enclosure for the rectifying element 2. The rectifying junctionor element 2 is formed of a pellet 7 of impurity element of appropriateconductivity type, which pellet is connected with an electrode or lead 8which terminates in a recess 6 in the sleeve 5.

The insulating member 4 may be of glass or ceramic material. When formedof ceramic material, as is preferable, it is provided with a shoulder 9on to which the rim of the metal sleeve 5 fits, the rim of the metalsleeve being secured to the ceramic member by means of a. solder whichunites with the rim of the metal sleeve and with a metallic film,previously provided on the surface of the shoulder on the ceramicmember. The ceramic member is then similarly united to the metal annulus3. When glass is employed in place of ceramic material, the glass ishermetically sealed by fusion to the metal annulus 3 and to the metalsleeve 5, the glass and metal being chosen to have a thermal expansioncharacteristic comparable with that of the metal members to which it issecured, and the metals being selected to form an hermetic joint withthe glass.

The rectifying element 2 may be secured to the metal base by means of alow melting point solder, the cooperating electrode 8 being secured tothe remote face of the rectifying element in such a way as to formthereat a rectifying junction. The procedure for forming such junctionsis now well-known and when germanium of N-type conductivity is used forthe rectifying element 2, the co-operating conductor may be secured tothe face of the germanium element with an interposed layer of indiumwhich forms the pellet 7.

The final steps in manufacturing such a rectifier are (a) to bringtogether the two parts, the one consisting of the base plate 1 with itsattached rectifying element 2 and co-operating electrode 8, and theother consisting of the metal annulus 3 with the metal sleeve securedthereto 5, through the intermediary of the annular insulating member 4;(b) to secure the flange on the metal annulus 3 to the base plate; (0)to secure the metal rod 8 extending from and forming part of theco-operating electrode, in the recess 6 in the metal sleeve 5, thusmaking electrical contact and securely holding it in position andpreventing subsequent disturbance of the co-operating electrode at itsjunction with the rectifying element.

The securing of the flange of the metal annulus to the base plate may beeffected by a pressure process using a layer of indium between theadjacent faces of the base plate and the flanged metal annulus. Thismethod forms no part of the present invention but is described andclaimed in co-pending application, Serial No. 586,090, by Alan JohnBlundell and Harry Roy Noon, and assigned to the assignee of the presentapplication.

In the securing of the metal rod 8 into the recess in the metal sleeve5, the wall of the sleeve is preferably crimped or pressed on to therod. To make it possible to press the wall of the metal sleeve 5 on tothe rod 8, a portion of the wall of the recess in the metal sleeve maybe made of reduced cross section, so as to render it readily deformable.The rod may be a hollow tube so that deformation is suflicient to give alarge electrical contact area.

In order to ensure that during the pressing of the wall of the metalsleeve on to the rod, no undue stress is imposed on the joint betweenthe co-operating electrode and the rectifying element, we prefer to formthe co-operating electrode of resilient material such as a braidedconductor, as shown in Fig. 2, or a flexible loop of wire or stripconductor, the conductor, wire or strip being secured to the metal rodso as to permit of slight relative movement between them during thefinal assembly operation.

During operation, it is desirable to ensure that the heat.

developed by "the passage of rectified current through the-rectifierelement'doesnot'cause undue heating of the element, and the metal base 1is accordingly made of a metal of good thermal conductivity, e. g.copper, and

"is ofsu'fficientthickness to 'removebyrconduction, the

heat developed at -the--rectifying element. To ensure that the heat 'soremoved-iydissipated, there may be provided in intimate contact with themetalbase,-a-radiating fin 10 of large-surface area,"securedinintimatecontact'with the =metal base. The "radiatingfinmay 'besecured-to the metal base-either by a low *melting point solder, oralter- "natively, as shown in"-Figs.' 4--to56, the'fin maybe clamped tothe metal-base,-using the external shoulder on the flan ged-'metal"annulus as "a seat on Which"a-*clarriping washerl-l -"(Figs.-'4and 6) or ring l'2"(Fig5) can 'be *located. "The "washer'or ringmay besecured to the fin by rivets as-shown in Fig.*5,-'or by bolts orthelike, -as' shown in Figs. 4 and 6. Thus,-for example, the 'fin may heprovided 'with a number of spaced cleat nuts-14 (Fig.4) -secured to it,-the-' nuts being engaged byscrews lithe=shanks=of which passthrough'the'annular clampingwasner 11 which enga'gcs the face of theflanged' metal annulus 3.

Whatd claim is: l. A P-N junction rectifier comprising 'a base memberconstitutedofa metal of high-electrical conductivity, a piece ofsemiconducting material'secur'ed at one face in intimate contact witha'face of said base member, an electrode electrically connected with theother face of said piece and forming therewith a rectifying junction,

a metal rod terminating saidelectrode, a flanged metal annulussurrounding said piece and hermetically secured at its flange totheface-of said-base'member to which said piece is secured, an annularceramic member hav- :constituted of .a metal of high electricalconductivity, a piece of semi-conducting material secured at one face inintimate contact with a face ofsaid base member, an electrodeelectrically connected with 'the other face of .said piece and formingtherewith a rectifying junction, a

flexible conductor secured-to said electrode at one end thereof, a.metal rod :secured to the other 'endof :said

flexible conductor, a flanged metal annulus surrounding .said pieceLandhermetically secured at its flange-t the faceof said base member-towhich said piece is seemed,

an annular cermic :member having one .face ssecured hermeticallytosthetrim ofsaidmetal annulus, said'ceramic rmember .being formed witha shoulder, a blind ametal sleeve .having acflange located .insaid-shoulder in said ceramic member andhermetically secured therein,said :metalsleeve havinga-central recess into which'said metal 'whereby"said metal "sleeve forms one terminal of' said rectifier and said mainbase member forms the other terminal of said rectifier;

3. A P-N junction rectifier comprising a base member constituted ofcopper, a' flake of monocrystalline germanium secured at one face inintimate contact with a face of said basermember, said flake containingan impurity element of one conductivity type, a conductor, one endof'said conductor being'secured'to the exposed face of said flake bymeans of a soldero-f a'low melting point impurity element'o'f oppositeconductivity type diffused into said flakerso astoform therewith arectifying junction, said conductor terminating in a metal rod, aflanged metal' annulus surrounding said piece and hermetically securedat its flange to the face of .said base member to which said piece issecured, an annular ceramic member having oneface secured hermeticallyto thelrim of said metal annulus, said ceramic member being formedwith ashoulder, a blind metal sleeve having a flange located in said shoulderin said ceramic member and hermetically secured therein, said metalsleeve having a central recess into which'said metal rod extends andwithin'which it:is frictionally secured, whereby said metal sleeve formsone terminal of ,said rectifier and said main base member forms theother terminal of said rectifier.

4. AP-N junction rectifier comprising a base member consisting of ametal of high'electrical conductivity, a

flake of monocrystalline semi-conductor material secured 'by means of alow melting point solder to one face of ,saidbase member, saidflakecontainingan impurity elementof one conductivity type, a flexibleconductor,-one

end of said conductor being secured to the-exposedface of saidflake'by'means of a'pellet of an impurity element .of oppositeconductivity type diffused into'said flakepso as to form therewith arectifying junction, the .other end .of said conductor being connectedtoone end of a metal rod, a flanged metal annulus surrounding said flakeand hermetically secured at its flange to the face of said base memberto Which'said flake is secured, an-annular ceramic insulator having oneface secured hermetically to the rim of said metal annulus, saidinsulator being formed with a shoulder, a blind flanged metal sleeveseated against said shoulder and hermetically secured therein by solder,said sleeve having an internal recess into which the other endof saidmetal rod extends, said sleeve being crimped to frictionallyssecure saidrod within the'sleeve, saidsleeve and said base member. forming theterminals of said rectifier.

References Cited in the file of this;patent UNITED STATES PATENT S

